Electrophotographic mateiral and process



United States Patent Ofiice Patented Apr. 5, 1966 16 Claims. 2C1. 96-1) Electrophotographic material normally consists of a support on which there is a photoconductive substance, this coating being provided with an electrostatic charge in the absence of light. The material is then exposed to light behind a master, or an episcopic image is projected thereon, so that an electrostatic image is formed which corresponds to the master. This image is developed by being briefly contacted with a resin powder, whereupon a visible image is formed which is fixed by heating or by the action of solvents. In this way, an image of the master which is resistant to abrasion is obtained electrophotographically.

For the photoconductive coatings, inorganic substances such as selenium, sulphur or zinc oxide have been used and organic compounds such as anthracene and anthraquinone have also been employed for this purpose.

In accordance with the present invention, a material for electrophotographic purposes is provided in which the photoconductive coating comprises one or more organic compounds each having at least two aromatic rings and at least one amino or alkylamino group, the aromatic rings being fused with a heterocyclic ring.

The supports for the photoconductive coatings are primarily foils made of metal, e.g., aluminum, zinc, copper; cellulose products such as paper and cellulose hydrate; cellulose esters such as cellulose acetate and cellulose butyrate; especially such esters which are partially saponified and plastics having a specific conductivity higher than 1(l ohm- .cm.'" such as polyvinyl alcohol, polyamides and polyurethanes.

A support useful for the preparation of the material of the present invention should he electroconductive. This term means in the present case that the support should have an electroconductivity which is suitable for electrophotographic purposes. Such supports comprise very good conductors, e.g., metal, as well as materials which have a relatively low conductivity and are no conductors in the usual sense, such as paper. The term electroconductive support in the meaning of the present case comprises supports which have a specific conductivity higher than ohm .cm. preferably high than 10 ohm .cm.

If paper is used as supporting material, it is preferably pretreated against the penetration of the coating solutions, e.g., it can be treated with a solution of methyl cellulose or polyvinyl alcohol in water or with a solution of an interpolymer of acrylic acid methyl ester and acrylonitrile in a mixture of acetone and rnethylethylketone, or with solutions of polyamides in aqueous alcohols or with aqueous dispersions of such substances.

Exemplary of the organic compounds used in the photoconductive coatings of the invention are 7-amino-3,9- benzo-phenazine, 7-ethylarnino-8,9-benzo-phenazine, 7- dimethylamino-8,9-benzo-phenazine, 2-3-diamino-phenazine, Z-amino-acridine, and 2-amino-9-hydroxy-acridinc, which have the following formulae respectively:

FORMULA 1 FORMULA 2 FORMULA 3 FORMULA 4 FORMULA 5 FORMULA 6 The preparation of the compounds is by the usual processes of organic chemistry, such as reduction of the corresponding nitro or nitroso compound or conversion of the corresponding halogen compounds into the amino compounds by means of ammonia or amino compounds or amines under conditions of heat and possibly increased pressure.

The compounds are very well suited for the production of photoconductive coatings and are generally colorless.

For the preparation of the electrophotographic material, the photoconductive amino compounds containing more than one aromatic nucleus are preferably dissolved in organic solvents such as benzene, acetone, methylene chloride, or ethylene glycol monomethylether or other organic solvents in which they are readily soluble, or in mixtures of such solvents. These solutions are coated upon the supporting material in the normal manner, e.g.,

by immersion processes, painting or roller application or by spraying. The material is then heated so that the solvent is removed.

A number of the compounds in question can be applied together to the supporting material or the compounds can be applied in association with other photoconductive substances.

Further, it is often advantageous for the compounds to be used in association with organic resins as photoconductive coatings. Resins primarily of interest for this purpose include naturalresins such as balsam resins, colophony and shellac, synthetic resins such as phenol resins modified with colophony, and other resins in which colophony constitutes the major part, coumarone resins, indene resins and those included under the collective term synthetic lacquer resins. According to the Saechtling-.Zebrowski Plastics Handbook, 11th edition, 1955, page 212 onwards, these include the following: processed natural substances such as cellulose ethers; polymers such as vinyl polymers, e.g., polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl ethers, polyacrylic and polymethacrylic acid esters, as also polystyrene and isobutylene and chlorinated rubber; polycondensates, e.g., polyesters, such as phthalate resin, alkyd resin, maleic resinate, maleic resin/colophony mixed esters of higher alcohols, phenol-formaldehyde resins, in particular phenol-formaldehyde resins modified with colophony, urea-formaldehyde condensates, melamine, formaldehyde resins, aldehyde resins, ketone resins, particularly so-called AWZ resins, xylene formaldehyde resins, polyamides and polyadducts such as polyurethanes. Also, polyolefins such as various polyethylenes and polypropylenes and phthalic acid polyesters, such as terephthalic and isophthalic acid ethylene glycol polyesters may be used.

If the photoconductive compounds are used in association with the resins described above, the proportion of resin to photoconductive substance can vary very greatly, but the content of photoconductive substance should be at least 20%. Mixtures of from 2 parts of resin and one part of photoconductive substance to two parts of photoconductive substance to one part of resin are preferred. Mixtures of the two substances in equal parts by weight are particularly favorable.

The solutions of the compounds, with or without the resins, are applied to the supports in the usual manner, for example, by painting, roller application, immersion processes or by spraying, and then dried. An even, homogeneous, transparent and, in most cases, colorless photoconductive layer is thus formed.

The light-sensitivity of these photoconductive coatings is in the long wave ultra-violet region, at about 3600- 4200 A. With high-pressure mercury vapor lamps, which transmit a large amount of ultra-violet rays, short exposure times can, however, be achieved.

The light-sensitivity of the photoconductive layer in the visible part of the spectrum, can be highly improved by the addition of sensitizers, so that even with ordinary light sources short exposure times can be achieved. Even very small additions, e.g., less than 0.01 percent, have considerable effect. In general, however, the amount of sensitizer" to be added to the photoconductive substance is from 0.01 to 5 percent, and preferably 0.1

stuffs, namely rhodamines, such as Rhodamine B (No. 864, p. 365), Rhodarnine 66 (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Sulphorhodamine B (No. 863, p. 364), and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No. 883, p. 375), Eosin A (No. 881, p. 374), Erythrosin (No. 886, p. 376), Phloxin (No. 890, p. 378), Bengal Rose (No. 889, p. 378), and Fluorescein (No. 880, p. 373); thiazine dyestufls such as Methylene Blue (No. 1038, p. 449) acridine dyestuffs such as Acridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypaflavine (No. 906, p. 386); quinoline dyestuffs such as Pinacyanol No. 924, p. 396) and Cryptocyanine (N0. 927, p. 397); quinone dyestuifs and ketone dyestuffs such as Alizarin (No. 1141, p. 499), Alizarin Red S (No. 1145, p. 502), and Quinizarine (No. 1148, p. 504); cyanine dyestuifs, e.g., Cyanine (No. 921, p. 394) and chlorophyll.

For the production of copies using the electrocopying material, the photoconductive coating is charged positively or negatively, by means of, for example, a corona discharge with a charging apparatus maintained at 6000- 7000 volts. The electrocopying material is then exposed to light in contact with a master or, alternatively, an episcopic or diascopic image is projected thereon. An

* electrostatic image corresponding to the master is thus produced on the material. This invisible image is developed by contact with a developer powder consisting of carrier and toner. The carriers used may be, for example, tiny glass balls, iron powder or tiny plastic balls. The toner consists of a resin-carbon black mixture or a pigmented resin of a grain size of l to 1000:, preferably 5 to 300:. The developer may also consist of a resin or pigment suspended in a non-conductive liquid in which resins may be dissolved. The image that now becomes visible is then fixed, e.g., by heating with an infra-red radiator to 170 C., preferably -150 C., or by treatment with solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol, or steam. Images corresponding to the master, characterized by good contrast eifect, are obtained.

After being fixed, these electrophotographic images can be converted into printing plates, if the support, e.g., paper, metal or plastic foils, is wiped over with a solvent for the photoconductive layer, e.g., alcohol or acetic acid, then washed down with water and inked up in known manner with greasy ink. In this way, printing plates are obtained which can be set up in an offset machine and used for printing.

If transparent supporting material is used, the electrophotographic images can also be used as masters for the production of additional copies on any type of light-sensitive sheets. Irt this respect, the photoconductive compounds provided by the invention are superior to the substances used hitherto, such as selenium or zinc oxide, inasmuch as the latter give only cloudy layers.

Furthermore, the photoconductive material of the present case has an improved photoconductivity which is superior to that of the known organic photoconductors, such as anthracene, benzidine and anthraquinone.

If translucent supports are used for photoconductive layers such as are provided by the invention, reflex images can be produced also. The electrophotographic material constituted in accordance with the invention has the advantage that it gives images rich in contrast and that it can be charged positively as well as negatively.

The invention will be further illustrated by reference to the following specific examples:

Example I 1 part by weight of the compound corresponding to Formula 2 (Eicker, Berichte der Deutschen Chemischen Gesellschaft, 23, (1890), p. 3804) and 1 part by Weight of colophony-forrnaldehyde resin (Corepal are dissolved in 30 parts by weight of benzene and applied to a paper the surface of which has been treated against the penetration of organic solvents and the coating is dried. Direct images can be produced on this paper by the electrophotographic process. After being charged by a corona discharge, with a negative polarity, the paper is exposed under a master to the light of a high-pressure mercury vapor lamp, and then dusted over in known manner with a developer consisting of a mixture of carrier and toner. The carrier used may consist of tiny glass balls, iron powder, and organic or inorganic substances. The toner consists of a resin-carbon black mixture or a pigmented resin of a grain size of 1-1000c, preferably 530oz. An image corresponding to the master is formed which is fixed by heating and is characterized by good contrast effect. By using a corona discharge having a positive polarity for the charging of the photoconductive layer and the same master and developer there are obtained reversal prints of the master. If transparent supports are used for the preparation of xerographic images, these can be used in known manner as masters for further copying on any type of light-sensitive sheets.

The compound corresponding to Formula 3 can be used instead of the compound corresponding to Formula 2.

Example 11 0.5 part by weight of the compound corresponding to Formula 1 (Fischer and Hepp, Berichte der Deutschen Chemischen Gesellschaft, 23, (1890), p. 845 and 2787), 1 part by weight of S-amino-acenapht'hene (Sachs and Mosebach, Berichte der Deutschen Chemischen Gesellschaft, 44, (1921), p. 2855) and 1 part by weight of resin-modified maleic acid resin (Beckacite K125) are dissolved in 3() parts by weight of benzene and applied to a superficialiy roughened aluminum foil. After evaporation of the solvent, the coating adheres firmly to the surface. The further procedure described in Example I is followed and, after fixing, a positive image is obtained on the aluminum foil. This image can be converted into a printing plate if the aluminum foil is wiped over with alcohol, Washed down with water and inked up with greasy ink in the presence of 1 percent phosphoric acid. A printing plate corresponding to the master is obtained; this can be set up in an offset machine and used for printing.

Example III 0.5 part by weight of the compound corresponding to Formula 4 (Fischer and Hepp, Berichte der Deutschen Chemischen Gesellschaft, 23, (1890), p. 2788), 0.5 part by weight of l-amino-anthracene (Von Braun and Bayer, Annalen der Chemie, 472, (1929) p. 113),

0.03 part by weight of Methylene Blue (Schultz, Far-bstofitabellen, 7th edition, (1931), No. 1038) and 1 part by weight of resin-modified maleic acid resin (Beckacite K105) are dissolved in a mixture of 20 parts by Weight of methylene chloride and 20 parts by weight of benzene. The solution is applied to a paper foil the surface of which has been treated against the penetration of organic solvents. The coating is dried; further procedure is as in Example I. An image corresponding to the master is obtained when the layer had been negatively charged. By switching the polarity of the corona discharge, reversal images of the same master can be obtained by means of the same toner.

The compound corresponding to Formula 5 may be used instead of the compound corresponding to Formula 4.

Example IV The procedure described in Example I is followed but for coating the paper, a solution is used consisting of 1 part by weight of the compound corresponding to Formula 6 (Ullman, Justus Liebigs Annalen der Chemie, 355, (1907), p. 335) and 1 part by Weight of ketone resin (Kunstharz EM) in 30 parts by weight of ethylenegiycol monomethylet-her. Images corresponding to the master are obtained.

in which R and R are selected from the group consisting of fused ring arylene groups and amino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings and at least one of R and R having at least one amino group linked thereto, and R is selected from the group consisting of OH =N, 1-, and =(I1 groups.

2. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the forand a compound selected from the group consisting of a dyestult sensitizer and a resin.

3. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a dyestuit sensitizer and a resin.

4. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the forand a compound seelcted from the group consisting of a dyestufl': sensitizer and a resin.

5. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula N NH;

\N/ NH2 '7 and a compound selected from the group consisting of a dyestuff sensitizer and a resin.

6. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a dyestufi sensitizer and a resin.

7. An electrophotographic material comprising a con ductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a dyestufif sensitizer and a resin.

8. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R and R are selected from the group consisting of fused ring arylene groups and amino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings and at least one of R and R having at least one amino group linked thereto, and R I is selected from the group consisting of =N-, 3-, and

groups.

9. A process according to claim 8 in which the photoconductive layer contains a dyestufi' sensitizer.

10. A process according to claim 8 in which the photoconductive layer contains a resin.

11. A photographic reproduction process which comprises exposing an electrically charged supported .photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula 12. A photographic reproduction process which comprises exposing an electrically charged supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconduc'tive layer comprising a compound having the formula 13. A photographic reproduction process which comprises exposing an electrically charged supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula 14. A photographic reproduction process which comprises exposing an electrically charged supported photoconductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula 15. A photographic reproduction process which comprises exposing an electrically charged supported photoconductive insulating layer to light under a master and developing the resulting image, the ph-otoconductive layer comprising a compound having the formula 16. A photographic reproduction process which comprises exposing an electrically charged supported photo conductive insulating layer to light under a master and developing the resulting image, the photoconductive layer comprising a compound having the formula References Cited by the Examiner UNITED STATES PATENTS Lyons et al.: Journal of the Chemical Society, August 1957, pp. 3648-3668.

Vartanian: Phys. Chem, U.S.S.R., 20, 1946, pp. 1065- 1080.

Vartanian: Acta Physicochimica U.S.S.R., 22, (1947), pp. 201-224.

Venkataraman, Synthetic (1952), pp. 755-760, 764-773.

Dyes, Academic Press NORMAN G. TORCHIN, Primary Examiner.

PHILIP E. MANGAN, HAROLD N. BURSTElN,

Examiners. 

1. AN ELECTROPHOTOGRAPHIC MATERIAL COMPRISING A CONDUCTIVE SUPPORT LAYR AND A PHOTOCONDUCTIVE INSULATING LAYER, THE LATTER COMPRISING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF A DYESTUFF SENSITIZER AND A RESIN, AND A COMPOUND HAVING THE FORMULA 